The present inventions are related to systems and methods for processing digital signals, and more particularly to systems and methods for analog to digital conversion.
Analog to digital converters are used in a number of semiconductor devices to convert an analog electrical signal to a digital representation thereof. In the conversion process, a continuous analog signal is converted to a series of discrete or quantized digital values representing the analog signal at defined sample times. Simple analog to digital converters operate over a specified, static range of operation typically defined to encompass an expected analog input signal. FIG. 1 depicts an exemplary prior art flash analog to digital converter 100. Flash analog to digital converter 100 includes a comparator bank 120 including a number of comparators 121, 122, 123, 124, 125 that each receives a respective reference threshold (i.e., ref(n−1), ref(n−2), ref(3), ref(2) and ref(1)). In addition, each of comparators 121, 122, 123, 124, 125 receives an analog input 105, and compares analog input 105 to the respective reference threshold. The reference thresholds are chosen such that the combined output of comparator bank 120 is a thermometer code indicated as a digital output 170. When operating properly, digital output 170 includes an uninterrupted series of 0's followed by an uninterrupted series of 1 s with the transition between 0 s and 1 s indicating the level of analog input 105 (i.e., a thermometer code without bubbles). In some cases, digital output 170 is provided to an encoder 180 that provides an encoded output 190 that may be more compact than a thermometer code.
In such a flash analog to digital converter, increased resolution is provided by reducing the level difference between successive reference voltages. Where the range of analog to digital converter 100 is to be maintained constant, increasing resolution requires a corresponding increase in the number of comparators. This has at least two disadvantages. First, additional comparators increase power and area consumption. Second, noise on analog input 105 and process differences in comparators 121, 122, 123, 124, 125 often results in production of an imperfect thermometer code (i.e., a thermometer code exhibiting bubbles) where the difference between successive reference voltages becomes small. Consequently, to compensate for the imperfections in the thermometer code, the complexity of encoder 180 increases substantially. This results in additional undesirable power and area costs.
Hence, for at least the aforementioned reasons, there exists a need in the art for advanced systems and methods for analog to digital conversion.